Investigation of Refractory Corrosion by Na2O–B2O3 Flux and Its Ability of Dissolving of Mn Oxides during a Melting Process for a Copper Alloy in the Atmosphere, Including Mn as Easily Oxidized Element

In order to clarify a guideline for designing of composition of a flux which can achieve both minimizing a refractory corrosion by the flux and maximizing of solubility of Mn oxides into the flux, corrosion tests for refractory was conducted in the air atmosphere. The basic composition of flux is Na2O–B2O3 and the refractory is Mullite (3Al2O3·2SiO2), assuming a process of melting of a copper alloy containing Mn as easily oxidized elements. Although the corrosion ratio of refractory became larger with increasing of mole fraction of Na2O in flux, the concentration of refractory’s constituents in the flux have different tendency predicted by the results of corrosion ratio. Through the corrosion test, the Na2O–B2O3 based flux has penetrated inside the refractory with Mn, and a part of that Mn has reacted with Al2O3 to form MnAl2O4. However, in the refractory/flux interface no clear formation of the compound layer could be confirmed due to the reaction between the refractory’s constituents and the flux. In addition, the relationship between the corrosion ratio and the equilibrium solubility of 3Al2O3·2SiO2 for Na2O–B2O3 flux calculated by thermodynamic database was investigated. The result shows that there are not clear relationships between them. The cause of this can be explained by the affection of corrosion inside the refractory by the penetration of the flux through the pores in the refractory. Furthermore, it was shown that the amount of Mn oxide dissolved in the flux was strongly affected by the viscosity of the flux by calculation.